1. Field of the Invention
The present invention relates to a method for making a flat panel display. Specifically, the present invention relates to a method for making a field emission display which has an improved barrier array.
2. Description of Prior Art
Field emission displays are well known in the art and are widely used since they have a small volume, low power consumption, high contrast ratio, large viewing angle and are suitable for mass production. In an FED device, electrons are emitted from tips formed on cathode electrodes by applying a voltage to the tips. The electrons impinge on a phosphor screen formed on a back of a transparent plate and thereby produce an image.
A conventional field emission display employs metal microtips as emitters. However, it is difficult to precisely fabricate extremely small metal microtips for the field emission source. This difficulty greatly limits miniaturization of a conventional field emission display. In addition, metal microtips themselves are prone to wear out after a long period of use.
Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56–58). Carbon nanotubes have excellent mechanical properties, high electrical conductivity, nano-size tips, and other advantages. Due to these properties, it has been suggested that carbon nanotubes could be an ideal material for field emission applications.
In both convention field emission displays that use metal microtips as emitters and in field emission displays that use carbon nanotubes as emitters, a barrier array is used to separate and insulate the cathode and the gate electrodes. To achieve superior display quality, the barrier array should be made with high accuracy and uniformity throughout the entire barrier array, and the material of which the barrier array is made should not be porous, since otherwise air may become trapped in the pores. Furthermore, such applications as field emission display demands that the barrier have a flat upper surface and highly accurate height. Thus manufacturing the barrier array is a critical step in making a field emission display.
The two main methods for making barrier arrays in the art are the screen printing method and the sandblasting method. In the screen printing method, a barrier array is formed by repeatedly screen printing and drying paste material on a substrate, and then baking the assembly. However, during the repeated printing and drying procedure, it is difficult to ensure that the barrier array has a flat upper surface and uniform height, and this leads to increases in production costs. In addition, it is also difficult to fabricate the barrier array to a high precision when using the screen printing method. Thus, screen printing is not suitable for mass production of high quality barrier arrays used in field emission displays.
In the sandblasting method, which is widely used, material for the barrier array is applied to a substrate at a predetermined thickness, and then dried. Then a protective film having the shape of the desired barrier array is formed on the assembly, or a sand blasting mask is attached to the assembly. Sand is injected at high pressure so that unwanted portions of the material are removed, thus forming the barrier array. Finally, the barrier array is baked. However, the whole manufacturing process takes a considerable time, and control of the sand injection must be highly accurate. The sandblasting method is not very reliable, and is also prone to contaminate the manufacturing environment with sand.
Other methods for making barrier arrays for flat panel displays comprise photolithography, molding, and casting. However, all these methods require mating of a substrate with suitable pastes, as well as drying and baking processes. This makes these methods unduly time-consuming. Furthermore, it is difficult to fabricate barrier arrays using these methods to a high precision.
As described above, these difficulties of barrier array manufacturing greatly limit mass production of field emission displays having high precision.